1. The Field of the Invention
The present invention relates generally to methods and apparatus for enhancing the performance of visual display units (VDU's) and more specifically relates to a variably adjustable contrast enhancing panel in the form of an electrochromic device disposed on a flexible glass microsheet and to the methods of making and using same.
2. The Relevant Technology
Many types of visual display units (VDU's) are known. They are variously shaped and sized and are utilized in varied and diverse applications. Typical VDU's include computer monitors, televisions, video games, watches and instrument displays. Some VDU's have glass display screens, such as cathode ray tubes (CRT's), while others have plastic, such as liquid crystal displays (LCD's). The display screens are often flat but may also be either cylindrically or spherically curved. In addition, the display screens are frequently layered with an antireflection coating because the materials of the display screen reflect light which then interferes with an operator's ability to perceive the visual image displayed on the screen.
The glass display screen, in general, provides an excellent scratch resistant surface and, during the fabrication process, is tolerant of broad vacillations in temperature and pressure and withstands the harmful effects of harsh chemical usage. One problem, however, is that the glass display screen requires careful handling because it is prone to breakage. Another problem is that the glass must be laboriously and meticulously cleaned, typically by grinding, buffing and polishing, in order to remove optical blemishes. Such cleaning is normally performed before an antireflective coating can be applied, for, if not, the cleaning process usually causes catastrophic failure in the coatings.
Yet deposition of antireflection coatings post-cleaning, and post-assembly of the VDU, is also problematic because deposition processes are typically performed in vacuum chambers on relatively low-profile items such as discrete glass or plastic components, glass sheets, or continuous plastic webs and are not accommodating to assembled VDU's which are comparatively large and bulky. Although specialized handling and processing techniques have been developed to permit antireflective, or other types of coatings, to be deposited directly onto the display screen surface of assembled VDU's, the techniques remain expensive and technically difficult. For these reasons, many VDUs with glass display screens have forgone the integration of an antireflection coating as part of the display screen and adopted a panel attachment, layered with an antireflection coating, for bonding to the surface of the display screen after the VDU is assembled.
Similar to display screens for VDU's, glass substrate panel attachments advantageously provide excellent hardness and scratch resistance and can also withstand a broad range of coating deposition process conditions, i.e., temperature, pressure, and chemicals. Glass substrates disadvantageously also require careful handling to avoid breakage or damage and their surface must likewise be meticulously cleaned and polished smooth before the deposition of optical coatings. If the glass substrate is a specially manufactured curved glass panel, even further complications arise. Such complications include difficulty in applying a uniform and evenly distributed optical coating to a surface thereof. Increases in care and expense in shipping and handling are also experienced because the panel is usually bulky and fragile. Moreover, since the curved glass is specially designed to fit a particular radius of curvature, the curved glass panel is commercially prevented from being adapted to other curved display screens which have a different radius of curvature.
In general, the attachment of glass panels to curved display screens is accomplished by, first, applying a layer of curable liquid adhesive directly to the display screen surface and, second, by applying the protective panel to the layer. The adhesive is then cured by exposure to ultraviolet light which passes directly through the panel. Once properly attached, the panel is effective for antireflection and protection. Although other convenient and cheaper attachment means exist, such as pressure sensitive adhesives (PSA), rigid glass panels are unable to utilize these adhesives because PSA requires a substantially unattainable degree of match in curvatures of radius between the panel and the curved display screen of the VDU.
In addition to being coated with an antireflection coating, panels are frequently coated with additional optical coatings possessing other desirable properties beyond that of antireflection. Such other properties include the elimination of static, contrast enhancement, electrical conduction and/or electrical insulation, and electromagnetic interference (EMI) shielding. With respect to contrast enhancement, it is known that certain optical coatings enhance contrast by effectively combating the visual degradation of the image on the display screen that occurs when VDU's are operated in a lighted environment. The degradation is glare and is caused by ambient light reflecting therefrom. The degradation is even more pronounced as the ambient light is more directed and brighter.
In other disciplines, electrochromic (EC) coatings are known to enhance contrast and have been used in varied and diverse applications. Such applications include memory, display and light transmission elements on windows and mirrors. In general, EC devices are electrically switchable optical devices arranged as a "stack" of materials deposited as individual thin films on a glass substrate to variably adjust light transmittance in response to a voltage stimulus applied across the stack. The voltage typically being about +/-1Vd.c. In use, the applied voltage creates an electric field across the stack of materials which correspondingly causes a reduction in the optical transmittance of light through the device or, in other words, causes absorption of the ambient light. When the voltage is reversed, the EC device is caused to return to its original state.
In view of the above, it will be appreciated that, although glass panel attachments possess both advantages and disadvantages, they are not entirely satisfactory. As such, it would be an advance to provide methods and apparatus for cost effectively enhancing the attachment of glass protective panels to curved display screens, for enhancing performance of VDUs by minimizing optical defects during attachment and by utilizing known coating deposition techniques, such as EC coatings, to allow variable adjustment of the contrast of a VDU.